1. Field of the Invention
The invention relates generally to computer main boards (motherboards) and, more particularly, to a detection circuit on computer main boards for clearing BIOS configuration memory.
2. Description of the Related Art
In the present digital era, computer equipment is an essential tool for information processing. As the electronic technology progresses, the functions of the computer diversify into numerous aspects, offering the user the possibility of, for example, modifying various parameters that define the working environment configuration of the computer. Computer systems typically include a set of built-in software routines called the basic input/output system (BIOS). The BIOS is a software interface between the system hardware and the operating system software. The BIOS facilitates programmer and user interaction with the system hardware. The BIOS is commonly coded onto a non-volatile memory such as a ROM (Read Only Memory) or a PROM (Programmable ROM) such as an EPROM (Erasable PROM), an EEPROM (Electrically Erasable PROM), a flash RAM (Random Access Memory) or any other type of memory appropriate for storing BIOS. The user therefore can set, for example, a personal password, types and addresses of peripheral components, and power management functions. The setting of the working environment configuration is conventionally activated when, while the computer is switched on, a user presses specific keys on the keyboard. Once the setting is completed, the set data are stored in the BIOS memory of the computer main board (or the motherboard as what is referred to commonly). This setting will be used as the working environment configuration in subsequent on-switches of the computer.
The BIOS memory (e.g., a PROM chip) typically has a significantly longer access time than standard DRAM (Dynamic RAM) or SRAM (Static RAM) used for PC main memories. DRAM chips with access times of about 70 ns and SRAM chips with access times below 25 ns are common. But EPROMs and other PROM types often need up to 200 ns before the addressed data is available. This is important because extensive BIOS routines for access to floppy and hard disk drives or the graphics adapters are often located in the slower PROM. Moreover, these routines are frequently called by the operating system or application programs, which therefore slows down the program execution. To resolve this problem, the BIOS is commonly copied, or shadowed, from the slower BIOS memory into the faster RAM of main memory so that the main memory is accessed instead of the BIOS memory.
To prevent the loss of the stored working environment configuration when the power is no longer supplied to the computer, the computer main board is usually provided with a battery that serves as auxiliary power supply. The battery provides a necessary power voltage to refresh the faster-type BIOS configuration memory and prevent the loss of data stored therein. On the other hand, it is also necessary for the user to be able to clear and/or modify the setting stored in the environment configuration memory. This function is particularly needed when, for example, the default setting of the BIOS has to be reloaded in the faster-type BIOS configuration memory, or when the previously set BIOS configuration has to be cleared because the user has forgotten his/her password and the computer consequently cannot correctly switch on.
The conventional clearing circuit is usually implemented via a jumper that turns the connection of a power terminal of the faster-type BIOS configuration memory to the ground. The faster-type BIOS configuration memory is thereby provided with an electrical discharge path to clear the configuration data stored therein. However, because the time of each batch of electrical discharge generated from the faster-type BIOS configuration memory is not uniform, some batches may need a longer electrical discharge time to achieve a complete clearing. As a result, if the user sets an electrical discharge time that is insufficiently long, the memory clearing may be incomplete. Furthermore, if the incompletely cleared memory zones happen to pass through the check sum, problems may subsequently occur, such as an abnormal working environment after on-switch of the computer, abnormal on-switch of the computer, or even impossibility of switching on the computer.